Polypropylene (“PP”) is widely used in the automotive industry as base polymer for a variety of internal (e.g., instrument panel) and external (e.g., body panels) components. Typically, polypropylene-based compositions must provide a properties profile that includes high stiffness, high toughness at low temperatures, high resistance to distortion at elevated temperatures (i.e. high Heat Distortion Temperature or HDT), a Class ‘A’ surface to provide an aesthetic appeal, low shrinkage and easy moldability, all at a competitive price to the manufacturer. A key requirement is a strong combination of high stiffness (rigidity) and high toughness at low temperatures (resistance to deformation). A representation of the stiffness/low-temperature toughness balance that is available today is illustrated in FIG. 1A, and summarized in Table 1, which is a plot of Notched Izod Impact strength (ISO 180) at sub-zero temperatures (typically −29° C.; range −20 to −40° C.), plotted against ambient temperature Flexural Modulus (ISO 178), for compositions with melt flow rate (“MFR”, 230° C., 2.16 kg) values in the range 10 to 30 g/10 min. The data encompass a broad range of current commercial products from a variety of suppliers. These products contain fillers, which contribute towards increased rigidity. Typically, mineral fillers such as talc are used.
Today's best automotive compounds displaying high stiffness (Modulus) and high low-temperature toughness (Impact Strength) fall in a region of the landscape, by way of a plot of −29° C. Notched Izod as a function of ambient temperature Flexural Modulus, bounded by a line connecting the data points for industry standards ADX5023 (Advanced Composites Inc.) and EF341-AE (Borealis), within or left (below) of this boundary line as depicted in FIG. 1A.
The automotive industry is looking for even higher-performing compositions, which would allow OEMs to continue light-weighting to improve fuel economy and reduce emissions. Cost reduction is also a primary driver, providing the impetus to advance the development of polyolefin-based compositions. To extend the stiffness/toughness boundary, will require the use of a high-crystallinity polypropylene matrix, combined with even higher-performing impact modifier and filler components. What is needed is a polypropylene-based composition that has a higher Modulus and Impact Strength.
Relevant publications include WO 2013/169325; an MOS-HIGE pamphlet published by Mitsui Plastics Inc. (2009); and a presentation “Hyperform HPR-803” by Milliken & Company (2010); U.S. Pat. No. 8,927,638; EP 1 548 054 A1; EP 2 386 602; U.S. Pat. Nos. 5,571,581; and 5,252,659.